1. Field of the Invention
The present invention concerns an apparatus for ejecting balls including: a frame supporting a ball holder which is adapted for supporting a ball; an ejecting arrangement adapted for ejecting the ball from the ball holder; and a control unit; the ejecting arrangement including a pivot arm which is pivotable about a shaft between a loaded position and a shooting position and having an impact face spaced apart from the shaft, where the ball holder and the impact face are arranged such that the ball is hit by the impact face during the working stroke of the pivot arm in a direction from the loaded position to the shooting position, the apparatus including a locking arrangement with a first locking member connected to the frame and a second locking member connected to the pivot arm for releasable retention of the pivot arm in the loaded position, and a pre-tensioning arrangement with a torsion spring for pre-tensioning the pivot arm by pivoting the pivot arm about a pivot shaft.
2. Description of Related Art
In connection with goalkeeper training in soccer, it has appeared advantageous to use an apparatus for ejecting balls against a goalkeeper. Hereby field players that otherwise would be bound by the task of shooting against the goalkeeper are freed, reserving them for their own practice. Moreover, better precision and repeatability of the single shots against the goalkeeper are achieved such that shots can be practiced from different position with preselected direction and speed.
An apparatus using a principle known from catapults where a pivot arm is pre-tensioned by a torsion spring is known. The pre-tensioned pivot arm is released and pivots with great force against a ball placed in a ball holder. Some of the energy in the pivot arm is transmitted to the ball by impact. The ball is thereby ejected from the apparatus. The pivot arm is stopped by impact against an end stop. It is a drawback of such apparatus that a large amount of energy is transmitted to the frame of the apparatus when the pivot arm strikes the end stop. The energy is transmitted to the frame whereby the apparatus is set into motion and the energy is typically absorbed by friction against the ground. It is therefore necessary to fasten the apparatus to the ground in order to avoid that the apparatus moves between the shots as otherwise it will be impossible to achieve the desired precision and repeatability between successive shots. However, it is difficult to fasten the apparatus on a soccer field and particularly on the tournament field of a club as a large number of fastening members are required, e.g., strong plugs that will leave unacceptably large damage on the ground. Moreover, the apparatus will be less mobile whereby it becomes time consuming and difficult to practice shots from different positions.
A disadvantage of an apparatus of the above type is that the pre-tensioned spring constitutes a safety risk during maintenance of the apparatus as inadvertent release of the spring may cause injury to service personnel. Furthermore, the pre-tensioning of the spring itself during mounting is associated with great danger to the personnel.
U.S. Pat. No. 5,911,214 discloses an apparatus for ejecting balls where the apparatus is provided with a shock absorber connected between the frame and the pivot arm for absorbing the energy released during braking of the pivot arm. The shock absorber includes a piston mounted in a cylindrical housing. The wall of the housing has a series of perforations distributed along the housing and dimensioned so that the shock absorber can absorb and discharge, respectively, air through the perforations, thereby gradually braking the pivot arm when it approaches the end of its stroke. This is a relatively complicated way of braking the pivot arm. Moreover, packings between the piston and the housing have to be replaced from time to time.
Furthermore, an apparatus of the type mentioned in the introduction is known from U.S. Pat. No. 7,066,846 B2. Similar to other prior art apparatus, in this apparatus, there will occur a simultaneous pre-tensioning during the pivoting of the pivot arm to its loaded position such that the full pre-tensioning is determined by the returning of the pivot arm from the shooting position to the loaded position. During the return pivoting to the loaded position, the pre-tensioning is built up to the maximum pre-tensioning which is attained in the loaded position. This requires a great power for return pivoting and entails a limitation in the possibility of varying the shooting power.